As is known, one blood constituent measuring device is an oximeter which is a photoelectric photometer utilized for measurement of the fraction of hemoglobin in blood which is in the form of oxygenated Hb, which fraction is normally expressed in percentage with the percentage value being referred to as the oxygen saturation of blood. Oximetry is discussed, for example, in an article entitled "Oximetry" by Earl H. Wood, William F. Sutterer and Lucille Cronin, appearing at pages 416-445, of Medical Physics, Vol. 3, O. Glasser, Ed., Year Book Medical, Chicago, Ill. (1960).
Various oximetry devices and methods have been heretofore suggested and/or utilized, and have included devices that are non-invasive in nature as well as devices wherein the emitted light was either passed through the sample or reflected therefrom to light sensors. In addition, oximetry devices and/or methods have heretofore been suggested and/or utilized that include a plurality of light emitters operating in the red and infrared regions. Such devices and/or methods are shown, for example, in U.S. Pat. Nos. 4,167,331, 4,086,915, 3,998,550, 3,804,539, 3,704,706 (single beam), 3,647,299, and 3,638,640.
With respect to oximetry devices and methods now known, accuracy and/or dependability have often presented a problem, as has a requirement for quite complicated circuitry.
With respect to such devices and methods, it has heretofore been found necessary, for example, to use logarithmic functions in order to determine the oxygen saturation of blood (see, for example, U.S. Pat. Nos. 4,167,331, 3,998,550, 3,804,539, and 3,638,640), take derivatives of the intensity of transmitted light (see, for example, U.S. Pat. No. 4,086,915), or have used three frequencies in conjunction with three synchronous detectors, peak detectors and a ratio circuit (see, for example, U.S. Pat. No. 3,647,299) in order to determine the oxygen saturation of blood. In addition, while a digital processor has heretofore been suggested as a part of oximeter apparatus to determine oxygen saturation of blood, the oximeter apparatus also included a logarithmic amplifier (see, for example, U.S. Pat. No. 4,167,339).
While oximetry devices and/or methods have heretofore been suggested and/or utilized, none of these devices and/or methods have proved to be completely satisfactory, and improvements have therefore still been needed with respect to such devices and/or methods. In addition, a need exists for measuring devices and methods for measuring other constituents of blood such as, for example, carboxyhemoglobin, carbon dioxide in blood and/or glucose in blood.